This is a paid asset, but now you can download Mesh to Terrain Free.
Detail this asset from Unity Store: Original Link
Mesh to Terrain v2.4 (Latest version)
Mesh to Terrain v2.2
Mesh to Terrain v2.1.6
Mesh to Terrain v2.1.5
Mesh to Terrain v2.1.4
Mesh to Terrain is a tool for easily and quickly converting a 3D terrain model created in 3ds Max, Terragen or any other editor to Unity Terrains.
Mesh to Terrain can convert textures to SplatPrototypes (Terrain Layers), generate terrain from several models and split the model into several terrains.
Features:
• Supports Unity v5.6 and higher
• Unlimited number of models and terrains to convert;
• Terrains are created in the same place where the meshes;
• Convert the textures of models to textures of terrain;
• Seamless result, when working with multiple terrains;
• Manually adding models or automatic detection of all models in the layer;
• No need to manually add the components of physics;
• Works with Relief Terrain Pack (optional);
• Built-in update system.
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